In the medical industry, it has become desirable to conduct analytical evaluations using easily handled sample cartridges. In general, the sample cartridges are used with an analytical base station. A liquid sample (typically blood) to be analyzed is put into the sample cartridge. The cartridge is then connected to the analytical base station (or module), for conduct of analytical analyses. In some instances, a calibrant solution or gel is also evaluated. Two commercially available types of analytical base stations for conduct of such analysis, are the IRMA Blood Analysis System (IRMA) and the Blood Analysis Portal system (PORTAL), both of which are available from Diametrics Medical Inc., of Roseville, Minn. 55113, the assignee of the present application.
General features of analytical systems such as IRMA and PORTAL are characterized, for example, in U.S. Pat. No. 6,066,243 ('243), assigned to Diametrics Medical Inc. the complete disclosure for the '243 patent is incorporated herein by reference. Improvements relating to liquid sample cartridges usable with such arrangements are described in: (a) abandoned U.S. application Ser. No. 10/160,329, filed May 30, 2002, and entitled “Cartridge arrangement, Fluid analyzer Arrangement and Methods” (the Thornberg, et al. application), now abandoned; (b) co-pending U.S. application Ser. No. 10/185,201, filed Jun. 28, 2002, entitled “Analytical Test Cartridge, and Methods” (the Kee Van Sin application); and (c) co-pending U.S. application Ser. No. 10/210,661 filed Jul. 31, 2002, and entitled “Apparatus and Method for Hematocrit Determinations” (the Blomberg, et al. application), each of which are currently assigned to the assignee of the present disclosure and are incorporated herein by reference, issued as U.S. Pat. No. 6,794,877.
In general, cartridges characterized in the references of the previous paragraph include various types of sensors therein, for evaluating characteristics of a fluid sample introduced into the cartridge. The sensors may be of various types including, for example, amperometric sensors.
In general, a conventional amperometric sensor includes three electrodes: a working electrode, a reference electrode, and an auxiliary electrode. Amperometric sensors can also include only two electrodes. The circuit is designed such that the potential between the reference electrode and the working electrode is set to a specific value. The value is generally selected for the particular component within the fluid to be analyzed. Under the specific value of the potential between the working and the reference electrode, an electrochemical reaction occurs that generates a current. The circuit causes current to flow to the auxiliary electrode to counter the current being generated by the electrochemical reaction, such that the potential between the working electrode and the reference electrode remains at the specific value and the electrochemical reaction continues.
If two or more amperometric sensors of this type were placed in the same fluid with the sensors operated or polarized simultaneously, current could flow between the sensors, and thus the sensors could interfere with one another. Therefore, improvements are desirable.